Known methods of forming light emitting devices, such as light emitting diodes (LEDs) and semiconductor lasers diodes, may include the use of periodic table of elements column III materials such as aluminum (Al), gallium (Ga) and indium (In). Nitrogen (N) is a column V material, and nitride compounds of column III materials may be semiconductive, may be known as III-nitrides, and may be used in light emitting device formation.
Such III-nitride materials may be formed on solid support substrates, such as sapphire (Al2O3) or silicon carbide (SiC), which may be known as semiconductor on insulator substrates. Sapphire may be the most widely used support material, but may have an issue with crystal lattice parameter mismatch with the III-nitride materials, which may in turn cause physical and electrical problems, such as crystal defects, strain and layer separation. Sapphire may also have a thermal mismatch issue with the III-nitride material, which may be known as a coefficient of thermal expansion (CTE) issue. Sapphire also has a relatively low thermal conductivity, which may lead to thermal reliability issues in operational devices and higher long term failure rates. Silicon carbide support substrates may have better thermal conductivity compared to sapphire, and thus may use simpler device packaging methods, but SiC nonetheless has CTE and lattice mismatch issues with the III-nitride materials. The use of a support material such as a free standing (FS) GaN wafer or a GaN template (e.g., GaN on sapphire), which as III-nitride materials may have a better lattice match with the single crystal III-nitride materials of the light emitting device and may result in superior device yields and function. However, GaN is relatively expensive whether used as a free standing (FS) wafer or formed on a substrate (i.e., a template).
Present III-nitride laser devices may use a light confinement layer located between the support substrate and the active laser device layer to improve the efficiency of light coupling in the laser diode to the light emission active location. The light confinement layer may be a relatively thick layer (for example 500 nm) of aluminum gallium nitride (AlGaN) since the difference in refractive index (Δn) between the AlGaN and the active device material used in the multi-quantum well may maximize the confinement factor (F). An example of an active device layer may include layers of indium gallium nitride interleaved with layers of gallium nitride (i.e., InGaN/GaN), to form a multiple quantum well structure. However, the lattice match between an AlGaN light confinement layer and either the GaN or the InGaN layers of the active device may not be sufficient for acceptable operation and yield.
The above noted issues of expensive support substrates, thermal and lattice mismatch between support substrates and the III-nitride materials of the light confinement layer and active light emitting layers, may decrease the fabrication yield, increase the cost, and prevent widespread acceptance of III-nitride based optical emission devices such as laser diodes.